This invention generally relates to systems and methods for remotely heating polymeric materials to selected temperatures by the dispersion of particulate ferromagnetic materials throughout the polymers whose Curie temperatures correspond to the selected temperatures of heating. Both the system and the method find particular application in the remote formation of joints in composite structures, and may be used to form plastic materials which are either recyclable, or separably heat degradable.
Thermosettable plastic materials for forming mechanical joints or other structures are known in the prior art. In their uncured state, such materials may resemble either viscous liquids, putty-like solids, or even flexible, tape-like materials which may be manipulated into a desired shape, and then heat-cured to form a tough plastic solid that assumes the shape that the uncured polymer was last manipulated into. These materials find particular application with respect to the construction of joints in composite structures, such as in the graphite composite frames of state-of-the-art aircraft.
Unfortunately, there are a number of drawbacks associated with the use of such thermosettable polymers to construct aircraft frames and other structures that significantly limits their usefulness. For example, at some stages of construction, it is desirable if not absolutely necessary that the heat used to thermoset the polymer be applied only locally to the specific area of the joint, as the application of such heat to the surrounding components may damage or degrade them. In such instances, the application of heat in the form of infrared radiation must be performed very carefully, and with appropriate shielding so as not to damage the surrounding components. Still other difficulties arise with respect to the inspection of the surrounding joints. As joints formed entirely of plastics and other composite materials are transparent to X-rays, it is not possible to inspect the joint for bubbles, cracks, or other quality-degrading discontinuities with the same kind of X-ray equipment used to inspect metallic joints. Finally, both of these aforementioned problems become exacerbated when it is necessary to perform the repair of a joint formed from such thermosettable, polymeric materials since the remote and focused application of the energy necessary to heat-cure the thermosetting plastic used in the repair becomes difficult, if not impossible, as does the ability to remotely inspect the repaired joint. While these problems might be overcome by the provision of polymeric materials that are remotely heatable to selected temperatures corresponding to the curing temperatures of the polymers, thus far no such polymers have been developed in the prior art.
Still another set of problems which might be solved by provision of selectively and remotely heatable plastic materials occurs in the area of recyclable and degradable plastic materials. Recyclable plastics are known in the prior art. Such plastic materials may be used as wrapping or packaging materials for food products and manufactured goods, and then separated from other solid waste materials after being discarded and finally melted back down into a raw plastic material suitable for reuse. However, the lack of a convenient way to separate such reusable plastics after they are commingled with other unrecyclable polymeric materials and solid wastes has severely limited the usefulness of recyclable plastics. And while degradable plastics are known, these plastics are likewise not easily separable from other plastic materials and solid waste which they may be commingled with upon disposal. Many known degradable plastics further suffer from the disadvantage of being vulnerable to degradation when such degradation is not desirable. Such problems might be solved by the provision of polymeric materials that, even when commingled with other materials, are separately heatable to a temperature corresponding to their fusion temperatures so that they might be melted out and separated from other solid wastes.
Clearly, there is a need for plastic materials which are selectively and remotely heatable to a desired temperature, and which are further relatively easy to separate after being commingled with other polymeric materials and solid wastes.